Chronic lung diseases such as Cystic Fibrosis (CF) and Chronic Obstructive Pulmonary Disease (COPD) are often associated with chronic bacterial infection (Gibson et al. 2013). This chronic bacterial infection is due to these patients having a highly compromised innate immune system that prevents the body from clearing infections from the lung, in turn leading to an increased, detrimental inflammatory response and remodelling of the lung tissue (Voynow et al. 2008). One such bacterium that is linked with chronic infection in both CF and COPD patients is Pseudomonas aeruginosa; once established, this bacterium is almost impossible for the patient to eradicate (Murray et al. 2007). The presence of P. aeruginosa and other bacterial pathogens such as Staphylococcus aureus and Burkholderia sp. in these patients has the effect of recruiting a high number of neutrophils to the sites of infection within the lung and, as such, increases the local concentration of the protease, neutrophil elastase (NE) (Voynow et al. 2008). This high level of NE overwhelms the body's natural defence to proteases—the antiprotease screen (Voynow et al. 2008). One such antiprotease that is affected by high levels of NE is human Secretory leukocyte protease inhibitor (SLPI).
Mature SLPI is an 11.7 kDa (107-amino acid) antiprotease of SEQ ID NO: 2 that is produced by a number of immune and epithelial cells and can be found in multiple areas of the body including the lungs (Seemüller et al. 1986; Voynow et al. 2008). The production of mature SLPI (from SLPI of SEQ ID NO: 1 that includes, at its N-terminus, a 25 residue signal peptide [UniProtKB/Swiss-Prot-P03973]) is triggered by a number of different factors including the presence of the bacterial endotoxin lipopolysaccharide (LPS), protease production and the presence of differing cytokines (Kammouni et al. 1997). In general, the role of mature SLPI is to protect the body's tissues from the detrimental effects of differing proteases. However, mature SLPI also has anti-bacterial and anti-viral properties (Doumas & Kolokotronis 2005; Hiemstra et al. 1996). Findings by Weldon et al. (2009) have shown that, when CF patients are chronically infected with P. aeruginosa, the associated increased level of NE has the effect of cleaving SLPI at two sites within the polypeptide, Ser15-Ala16 and Ala16-Gln17 (Weldon et al. 2009), resulting in two species of C-terminal polypeptide fragments:
Species 1 (Q17-A107) (10,152 Da)—Weldon et al. 2009 (SEQ ID NO: 3)
QCLRYKKPECQSDWQCPGKKRCCPDTCGIKCLDPVDTPNPTRRKPGKCP VTYGQCLMLNPPNFCEMDGQCKRDLKCCMGMCGKSCVSPVKASpecies 2 (A16-A107) (10,223 Da)—Weldon et al. 2009 (SEQ ID NO: 4)
AQCLRYKKPECQSDWQCPGKKRCCPDTCGIKCLDPVDTPNPTRRKPGK CPVTYGQCLMLNPPNFCEMDGQCKRDLKCCMGMCGKSCVSPVKA.
The term “C-SLPI” as used herein, describes species 1 and 2 above (SEQ ID NOs: 3 and 4) that are each the C-terminal cleavage product of mature SLPI, cleaved by NE, each of which having significantly reduced biological activity in comparison with full length mature SLPI (Weldon et al. 2009).
Weldon et al. 2009 identified C-SLPI of SEQ ID NOs: 3 or 4 as being a potential biomarker for bacterial infection in, for example, CF patients. As such, C-SLPI of SEQ ID NOs: 3 or 4 have the potential for commercial exploitation as a test for bacterial infection. The aim of this test would be to improve on the current laborious and time-consuming classical microbiological diagnostic approach. The advantage of this would be to speed up diagnosis, so that treatment could be initiated more expediently and, therefore, reduce the lung pathology associated with bacterial infection.
The inventors describe herein antibodies with a unique specificity for C-SLPI of SEQ ID NOs: 3 or 4.